Both the blue-chip index and the S&P 500 posted their biggest one-day percentage drops since November 2011, with the Dow closing 10% below its recent high. U.S. oil prices also briefly dropped below $40 a barrel on Friday, a level not seen since the financial crisis.

Signs of a sharp slowdown in the world’s second-largest economy have unnerved investors since Beijing surprised markets last week by devaluing its currency. Shares in the U.S., Asia and Europe have tumbled, along with commodity prices as investors fretted about waning Chinese demand just as supplies are surging.

The Dow Jones Industrial Average declined 531 points, or 3.1%, to 16459.75. The S&P 500 dropped about 3.2% to 1970.89. The Nasdaq Composite shed 3.5% to 4706.04.

The market needs to drop 20% to get to bear market territory, which some U.S. stocks have already hit: